An SMPS actively regulates its output voltage by switching the output on and off in a duty cycle. The output of the SMPS may be given by the relative duration of the on and off portions of the duty cycle. This may be in contrast to linear power supplies, wherein power is dissipated in, for example, a transistor. SMPSs may be implemented as, for example, buck converters, boost converters, or buck-boost converters. An SMPS may regulate output voltage or current by switching ideal storage elements such as inductors and capacitors into and out of different electrical configurations. If a power source, an inductor, a switch, and the corresponding electrical ground are placed in series and the switch is driven by a square wave, the peak-to-peak voltage of the waveform measured across the switch can exceed the input voltage from the DC source. This is because the inductor responds to changes in current by inducing its own voltage to counter the change in current, and this voltage adds to the source voltage while the switch is open. If a diode-and-capacitor combination is placed in parallel to the switch, the peak voltage can be stored in the capacitor, and the capacitor can be used as a DC source with an output voltage greater than the DC voltage driving the circuit. This boost converter acts like a step-up transformer for DC signals. A buck-boost converter works in a similar manner, but yields an output voltage which is opposite in polarity to the input voltage. Other buck circuits exist to boost the average output current with a reduction of voltage. In an SMPS, the output current flow depends on the input power signal, the storage elements and circuit topologies used, and also on the modulation and duty cycle to drive the switching elements. The spectral density of these switching waveforms has energy concentrated at relatively high frequencies. As such, switching transients and ripple introduced onto the output waveforms can be filtered with a small LC filter.